Foundations for Hierarchical Full-duplex Networks

NSF NeTS Large (Grant #1314937)

Principal Investigators (Rice) : Ashutosh Sabharwal (PI), Edward Knightly and Lin Zhong
Principal Investigator (OSU) : Ness Shroff
Principal Investigator (UCLA): Suhas Diggavi

This page only describes results related to this NSF Grant, and is part of the larger full-duplex effort at Rice.
Click on tabs below for more information

PostDoctoral Researchers : John Tadrous (Rice), Changhee Joo (OSU)

Graduate Students : Xu Du (Rice), Andrew Kwong (Rice), Xing Zhang (Rice), Ryan Guerra (Rice), Yasaman Ghasem Pour (Rice), Clayton Shephard (Rice), Adriana Flores (Rice), Can Karakus (UCLA), Joyson Sebastian (UCLA), Zhenzhi Qian (OSU), Fei Wu (OSU), Yang Yang (OSU)

Past Participants : Evan Everett (Former NSF Grad Fellow, Rice, PhD'16), Jingwen Bai (Rice, PhD'16)

Research Experience for Undergraduates : James Grinage (Sophomore), Yoseph Maguire (Senior), Anant Tibrewal (Senior), Peter Washington (Former, now Graduate Student at Stanford University)

SoftNull Dataset

Pictures from SoftNull Experiments at NASA

Experiments performed by Evan Everett (Advisor: PI Sabharwal) and Clay Shepard (Advisor: PI Zhong)

NASA Array with Argos Backend
NASA Array with Argos Backend

Anechoic Chamber Experiments

Outdoor Experiments

Indoor Experiments

Pictures from Ongoing Experiments at Rice

Experiments performed by Xu Du, Xing Zhang (Advisor: PI Sabharwal) and Clay Shepard (Advisor: PI Zhong)

NASA Array with Argos Backend
NASA Array in Rice Labs (a huge thanks for their support !!)

Re-arranged array
Array elements re-arranged with uniform spacing of 0.5 λ

Indoor at Rice
Indoor Experiments in Duncan Hall, Rice University

Outdoor at Rice
Nighttime Outdoor Experiments on Rice Campus

Project Goals: In this project, we will develop foundational principles for hierarchical wireless network design by leveraging full-duplex transmissions in both access and wireless backhaul. Full-duplex is most promising at shorter ranges, and hence is fortuitously aligned with the predicted dominant access range in future networks. Furthermore, larger full-duplex ranges are feasible in infrastructure-to-infrastructure links, and hence are well suited for backhaul links. While full-duplex is well-aligned with the key elements of hierarchical networks, our current design principles are largely developed for half-duplex transmissions which is the basis for all current networks. The project goals are to develop data-driven signal models for full-duplex to facilitate information-theoretic analyses and foundations for network-scale resource allocation. The project will heavily leverage Rice WARP platform and Rice Argos platform. Our objectives fall in three broad inter-related thrust areas. In each case, we will develop solutions that ensure low complexity and low communications overhead.

  1. Signal-Scale Foundations for Full-duplex Networks: Full-duplex transmissions induce self interference, which is a near-field reception compared to all other receptions which happen in far-field. Our goal here is to develop data-driven signal models for self-interference and use the resulting models to develop signal-scale (PHY) foundations for hierarchical MIMO full-duplex networks.
  2. Theoretical Foundations for Full-duplex Network Scale Resource Allocation: Our second research goal is to develop scheduling and routing foundations for hierarchical full-duplex networks, by leveraging full-duplex self-interference cancellation. In addition to the physical layer gains obtained through multiple antennas, the promise of full-duplex lies in the potential for developing simpler algorithms because the half-duplex link activation constraint is eliminated.
  3. Protocols and Prototypes for Network Scale Full-duplex Resource Management: Our goal here is to develop practical protocols and construct operational network prototypes to translate the theoretical foundations into principles for deployment, using a combination of analysis and at-scale experimental evaluations.

The research results till date are organized in three sections below. The summary is written to provide an accessible overview of results, with details in related publications (click on publication tab to access cited publications).

Signal Scale Foundations

The over-riding theme in this research thrust is the novel use of spatial (antenna) resources in performing full-duplex beyond the envisioned use.
  1. Distributed Full-duplex (Collaboration between PIs Sabharwal and Diggavi): Full-duplex is much more challenging on small form factor devices, and hence it is possible that full-duplex capability may be limited to base-stations. In this case, full-duplex base-stations can simultaneously communicate with two devices - one uplink and another downlink. This introduces both self-interference at base-station and inter-node interference between mobile devices. We proposed distributed full-duplex where uplink & downlink communications happen on the main channel (e.g. the cellular channel) and devices cooperate on a separate orthogonal channel (e.g. the unlicensed bands). In a series of papers, we have
    • studied the feasibility of such a scheme, and showed that in many scenarios of interest, there is a high probability of finding open ISM band [C15].
    • devised novel methods and analyzed their information theoretic performance to manage device to device interference in a sequence of papers [C3,J2,J5]
  2. SoftNull - Massive MIMO Full-duplex: (Collaboration between PIs Sabharwal and Zhong) A key challenge in full-duplex is the need for new analog components, namely for analog cancellation. The analog complexity increases as the number of antennas increase, e.g. in Massive MIMO systems.
    SoftNull is a digital precoder to reduce self-interference and eliminate analog components based canceller
    We proposed transmit side beamforming to enable full-duplex capabilities in Massive MIMO. We first developed theoretical foundations that showed the degrees of freedom benefits in idealized systems [C9,J8]. Then we developed SoftNull to enable full- duplex in many-antenna systems. Unlike most designs that rely on analog cancelers to suppress self- interference, SoftNull relies on digital transmit beamforming to reduce self-interference. SoftNull does not attempt to perfectly null self-interference, but instead seeks to reduce self-interference sufficiently to prevent swamping the receiver's dynamic range. Residual self-interference is then cancelled digitally by the receiver. We evaluate the performance of SoftNull using measurements from a 72-element antenna array in both indoor and outdoor environments. We find that SoftNull can significantly outperform half- duplex for small cells operating in the many-antenna regime, where the number of antennas is many more than the number of users served simultaneously. See [J15] for more details.
  3. Reducing Control Overhead with Full-duplex : Till date, most studies have focused on spectral efficiency increase in full-duplex systems by bi-directional data communications. However, control channels consume a fair bit of resources in actual systems and hence reduction in control overhead is a high research priority. In our ongoing work, we are leveraging full-duplex to reduce control channel overhead. Our first line of contributions is reducing the overhead of channel state feedback for downlink multi-user beamforming. In [C13,C22], we developed the idea of continuous feedback for sequential beamforming that update beamforming weights while also performing downlink transmission. The resulting system has complex interference patterns. We show that despite the increased interference, the resulting system can outperform feedback systems that rely on half-duplex.
  4. Non-linear Distortion in Full-duplex: In full-duplex systems, due to the strong self-interference signal, system nonlinearities become a significant limiting factor that bounds the possible cancellable self-interference power. In [C5], a self-interference cancellation scheme for full-duplex orthogonal frequency division multiplexing systems is proposed. The proposed scheme increases the amount of cancellable self-interference power by suppressing the distortion caused by the transmitter and receiver nonlinearities. An iterative technique is used to jointly estimate the self-interference channel and the nonlinearity coefficients required to suppress the distortion signal. The performance is numerically investigated showing that the proposed scheme achieves a performance that is less than 0.5dB off the performance of a linear full-duplex system.

Theoretical Foundations for Network Operation

In this research thrust, our focus is development of theoretical foundations to analyze the network impact of full-duplex communications.
  1. Multi-cell capacity analysis (Collaboration between PIs Sabharwal and Diggavi) While it is easy to show that full-duplex will increase spectral efficiency in small 2 or 3 node networks, it is unclear if the benefits translate to network-scale operations. In our ongoing work [C2,C4,C16], we have started to lay the foundations for multi-cell analysis of full-duplex operation. To summarize our work in [C16], we first characterize the degrees-of-freedom of a multiuser MIMO (MU-MIMO) full-duplex network with half-duplex mobile clients, and derive the regimes where the inter-mobile interference can be mitigated to yield significant gains over the half-duplex counterpart. The achievability is based on interference alignment and requires full channel-state information at the transmitter (CSIT). Next, we study the case with partial CSIT where only the base-station acquires downlink channel values to avoid collecting network-wide CSIT at all transmitters in the system. We show that the key to achieving the sum degrees-of-freedom upper bound with only partial CSIT is the ability of the base-station to switch antenna modes that can be realized via reconfigurable antennas.
  2. Name (Collaboration between PIs Shroff and Sabharwal) Answered a fundamental question about the capabilities of full duplex versus other multi-antenna technologies. In particular, we have precisely characterized the conditions under which these technologies outperform each other for a general network topology under a binary interference model. This is the first work of its kind to precisely characterize the conditions under which these technologies outperform each other for a general network topology under a binary interference model. The analytical results were also are validated using a testbed with software-defined radios.

Network Protocols and Prototypes

In this thrust, we are translating the insights from first two thrusts into practical protocols that are benchmarked with a combination of analysis, simulations and testbed-based evaluations.
  1. Distributed Protocols for Managing Interference (Collaboration between PI Sabharwal and Prof. Lim of GIST, Korea): In distributed access systems like WiFi, it is not obvious how the information theoretic gains can be translated into practical gains since there is no central entity which has full network level knowledge. In [J17], we proposed a random-access medium access control protocol using distributed power control to manage inter-client interference in wireless networks with full-duplex capable access points that serve half-duplex clients. Our key contributions are two-fold. First, we identify the regimes in which power control provides sum throughput gains for the three-node atomic topology, with one uplink flow and one downlink flow. Second, we develop and benchmark PoCMAC, a full 802.11-based protocol that allows distributed selection of a three-node topology. The proposed MAC protocol is shown to achieve higher capacity as compared to an equivalent half-duplex counterpart, while maintaining similar fairness characteristics in single contention domain networks. We carried out extensive simulations and software-defined radio-based experiments to evaluate the performance of the proposed MAC protocol, which is shown to achieve a significant improvement over its half-duplex counterpart in terms of throughput performance
  2. Flores and Knightly introduced MUSE, the first system to achieve full-rank uplink multi- user capacity in a fully distributed and scalable manner without a control channel. MUSE is the first PHY and MAC system that enables scalable full-rank uplink multi-user multiplexing without requiring a control channel. In MUSE, no control messages are used for channel estimation, CSI feedback and channel-based user selection. The Knightly team designed MUSE-PHY which decorrelates users' signals through Arbitrary Cyclic Shift Delays, enables preamble-based clean channel estimation at the receiver with the Dynamic Orthogonal Mapping matrix and adapts to variable traffic demand of distributed transmitters. The team designed a fixed-overhead scalable MUSE-MAC that enables a multi-user multi-stream transmission through a single medium access contention. MUSE-MAC attaches a random set of additional users to the winning-user and assures the rank of the group equals the number of antennas at the AP. The researchers experiments demonstrated full-rank multiplexing gains in the evaluated scenarios that show linear gains as the number of users increase. Our experimental results show an average PHY capacity utilization of 197%, 290% and 395% for 2 to 4 concurrent users respectively with evaluated rates and maintain constant overhead as the number of users increases.
  3. (PI Shroff) Developed a the first fully distributed throughput-optimal scheduling algorithm for cut-through transmissions. This approach is based on a novel method to characterize the interference relationship between links in the network with cut-through transmission, which allows decoupling of the routing and scheduling decisions for full-duplex communication with cut-through routing. This resolves the open problem of cut-through routing where the MAC layer rate region of the cut-through enabled network is directly a function of the routing decision, leading to a strong coupling between routing and scheduling. This approach also resolves the difficult question of how to dynamically form/change cut-through routes based on the traffic rates and patterns.
  4. (PI Shroff) Developed the first known multicast transmission/feedback technique which approaches the optimal throughput with a constant feedback overhead independent of the number of receivers. This is in contrast to traditional approaches (that have impeded practical multicast deployments) that either achieve high throughput at the cost of prohibitively large (e.g., O(n)) feedback overhead, or achieve low feedback overhead but without either optimal or near-optimal throughput guarantees.

PI Activities

Graduate and Post-doc Training


[J18] C. Karakus and S N. Diggavi, Enhancing Multiuser MIMO Through Opportunistic D2D Cooperation. Under review, IEEE Journal of Selected Areas in Communications.
[J17] W. Choi (GIST, South Korea), H. Lim (GIST, South Korea) and A. Sabharwal, Power-Controlled Medium Access Control Protocol for Full-Duplex WiFi Networks, IEEE Transactions on Wireless Communications, 14(7), pp. 3601-3613, July 2015 (Open Access).
[J16] C. Tian, J. Chen, S N. Diggavi and S. Shamai, Matched Multiuser Gaussian Source-Channel Communications via Uncoded Schemes. Under review, IEEE Transactions on Information Theory.
[J15] E. Everett, C. Shepard, L. Zhong, A. Sabharwal, Measurement-driven Evaluation of All-digital Many-antenna Full-duplex Communication, submitted to IEEE Transactions on Wireless Communications, August 2015.
[J14] W. Ouyang, J. Bai, A. Sabharwal, Leveraging One-hop Information in Massive MIMO Full-Duplex Wireless Systems, submitted to IEEE/ACM Transactions on Networking, August 2015.
[J13] Dominique Tschopp, Suhas N. Diggavi, Matthias Grossglauser, Hierarchical Routing over Dynamic Wireless Networks. Random Structures and Algorithms (RSA). 47 (4), 669-709, 2015.
[J12] R. Kolte, A. Ozgur, S N. Diggavi, When Are Dynamic Relaying Strategies Necessary in Half-Duplex Wireless Networks? in IEEE Transactions on Information Theory 61(4):1720-1738, June 2015.
[J11] F. Wu, Y. Sun, Y. Yang, K. Srinivasan, and N. B. Shroff, Constant Delay and Constant Feedback Moving Network Coding for Wireless Multicast: Design and Asymptotic Analysis, IEEE Journal on Selected Areas in Communications, vol. 33, Issue 2, Mar. 2015, pp. 127 - 140.
[J10] C. Karakus, I-H. Wang and S N. Diggavi, Gaussian Interference Channel with Intermittent Feedback, IEEE Transactions on Information Theory, 61 (9), 4663-4699, 2015.
[J9]S. Saeedi, V. Prabhakaran and S N. Diggavi, Capacity Results for Multicasting Nested Message Sets over Combination Networks, In revision, IEEE Transactions on Information Theory, January 2016.
[J8] E. Everett and A. Sabharwal, Spatial Self-Interference Isolation for In-Band Full-Duplex Wireless: A Degrees-of-Freedom Analysis In revision, IEEE Transactions on Information Theory, 2014.
[J7] A. Sabharwal, P. Schniter, D. Guo, D. Bliss, S. Rangarajan, R. Wichman, In-band Full-duplex Wireless: Challenges and Opportunities, IEEE JSAC Special Issue on Full-duplex Wireless Communications and Networking, October 2014.
[J6] P. Murphy (Mango Communications), C. Shepard, L. Zhong, A. Sabharwal and C. Dick (Xilinx), FPGAs help Massive MIMO Channels, Xilinx XCell Magazine, 89, Autumn 2014.
[J5] J. Bai, C. Dick and A. Sabharwal, Vector Bin-and-cancel for MIMO Distributed Full-duplex, in revision, IEEE Transactions on Information Theory, Jan 2014.
[J4] E. Everett, A. Sahai and A. Sabharwal, Passive Self-Interference Suppression for Full-Duplex Infrastructure Nodes, IEEE Transactions on Wireless Comm, Feb 2014.
[J3] A. Sahai, G. Patel, C. Dick and A. Sabharwal, On the Impact of Phase Noise on Active Cancelation in Wireless Full-Duplex, IEEE Transactions on Vehicular Technology, November 2013.
[J2] J. Bai and A. Sabharwal, Distributed Full-duplex via Wireless Side-channels: Bounds and Protocols, IEEE Transactions on Wireless Comm, August 2013.
[J1] E. Ahmed, A. Eltawil and A. Sabharwal, Rate Gain Region and Design Tradeoffs for Full-duplex Wireless Communications, IEEE Transactions on Wireless Communications, July 2013.


[C27] Joyson Sebastian, Can Karakus, Suhas Diggavi, Approximately achieving the feedback interference channel capacity with point-to-point codes. IEEE International Symposium on Information Theory (ISIT), July 2016.
[C26] A. Flores, S. Quadri, E. Knightly, A Scalable Multi-User Uplink for Wi-Fi in Proceedings of NDSI 2016, March 2016.
[C25] J. Tadrous, A. Sabharwal, Interactive smart-phone app traffic: an action-based model and data driven analysis, submitted to the 14th International Syposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt 2016).
[C24] C. Shepard, A. Javeed, L. Zhong, Control channel design for many-antenna base stations, Proceedings of the ACM International Conference on Mobile Computing and Networking (MobiCom), September 2015. [C23] Joyson Sebastian, Can Karakus, Suhas Diggavi, I-Hsiang Wang, Rate Splitting is Approximately Optimal for Fading Gaussian Interference Channels. Allerton conference, 315-321, September 2015.
[C22] Xu Du, John Tadrous, Chris Dick, and Ashutosh Sabharwal, MU-MIMO beamforming with full-duplex open-loop training, The 16th IEEE International Workshop on Signal Processing Advances in Wireless Communications, SPAWC 2015, July 2015 .
[C21] C. Tian, J. Chen, S N. Diggavi and S. Shamai, Matched Multiuser Gaussian Source-Channel Communications via Uncoded Schemes. IEEE International Symposium on Information Theory, June 2015.
[C20] X. Zhang, J. Tadrous, F. Xue, E. Everett, A. Sabharwal, Angle of arrival based beamforming schemes for massive MIMO FDD systems, in Proceedings of the 2015 IEEE Asilomar Conference on Signals, Systems and Computers (ASILOMAR), November 2015.
[C19] A. Kwong and A. Sabharwal, Overcoming Conjugate Beamforming Limitations with Side-Channel Cooperative Decoders, in Proceedings of the 2015 Asilomar Conference on Signals, Systems and Computers, November 2015.
[C18] Y. Yang and N. B. Shroff, Scheduling in Wireless Networks with Full-Duplex Cut-through Transmission, IEEE INFOCOM'15, Hong Kong, April 2015.
[C17] C. Karakus and S N. Diggavi, Opportunistic scheduling for full-duplex uplink-downlink networks, IEEE International Symposium on Information Theory, Hong Kong, June 2015.
[C16] J. Bai, S N. Diggavi and A. Sabharwal, On the degrees-of-freedom of multi-user MIMO full-duplex network IEEE International Symposium on Information Theory, Hong Kong, June 2015.
[C15] J. Bai, C. Liu, A. Sabharwal, Increasing cellular capacity using ISM band side-channels: a first study, In Proceedings of the 4th workshop on All things cellular: operations, applications, & challenges (AllThingsCellular '14). ACM, New York, NY, USA, 9-14.
[C14] Y. Yang, B. Chen, K. Srinivasan, N. B. Shroff, Characterizing the Achievable Throughput in Wireless Networks with Two Active RF chains, in Proceedings of the IEEE INFOCOM'14, Toronto, Canada, April 2014.
[C13] Xu Du, John Tadrous, Chris Dick, and Ashutosh Sabharwal, MIMO broadcast channel with continuous feedback using full-duplex radios, IEEE Asilomar Conference on Signals, Systems and Computers (ASILOMAR), pp.1701,1705, 2-5 Nov. 2014.
[C12] A. Flores and E. Knightly, Virtual Duplex: Scaling Dense WLANs and Eliminating Contention Asymmetry, in Proceedings of IEEE Workshop on Cognitive Radio Architectures for Broadband, Raleigh, NC, October 2014
[C11] J. Chen, A. Ozgur, S N. Diggavi, Feedback through Overhearing, Allerton conference, October 2014.
[C10] S. Mishra, I-H. Wang and S N. Diggavi, Harnessing Bursty Interference in Multicarrier Systems with Feedback, IEEE International Symposium on Information Theory (ISIT), July 2014.
[C9] E. Everett and A. Sabharwal, A Signal-Space Analysis of Spatial Self-Interference Isolation for Full-Duplex Wireless, IEEE International Symposium on Information Theory (ISIT), July 2014.
[C8] J. Hachem, N. Karamchandani and S N. Diggavi, Multi-level Coded Caching, in IEEE International Symposium on Information Theory (ISIT), July 2014.
[C7] S. Brahma, M. Duarte, A. Sengupta, I-H. Wang, C. Fragouli, S N. Diggavi, QUILT: A Decode/Quantize-Interleave-Transmit Approach to Cooperative Relaying, Proceedings of the IEEE INFOCOM, Toronto, Canada, April 2014.
[C6] Y. Yang, B. Chen, K. Srinivasan, N. B. Shroff, Characterizing the Achievable Throughput in Wireless Networks with Two Active RF chains, Proceedings of the IEEE INFOCOM'14, Toronto, Canada, April 2014.
[C5] E. Ahmed, A. Eltawil and A. Sabharwal, Self-interference Cancellation with Nonlinear Distortion Suppression for Full-duplex Systems, Asilomar Conference on Signals, Systems and Computers, November 2013.
[C4] A. Sahai, S. N. Diggavi and A. Sabharwal, On Uplink/Downlink Full-Duplex Networks, in Proc. Asilomar Conference on Signals, Systems and Computers, Pacific Grove, CA, November 2013.
[C3] J. Bai and A. Sabharwal, K-user Symmetric MIMO Distributed Full-duplex Network via Wireless Side-channels, IEEE Allerton Conference on Communication, Control, and Computing, October 2013.
[C2] A. Sahai, S. N. Diggavi and A. Sabharwal, On Degrees-of-freedom of Full-duplex Uplink/downlink Channel, IEEE Information Theory Workshop, September 2013.
[C1] C. Karakus, I-H. Wang, S N. Diggavi, An achievable rate region for Gaussian interference channel with intermittent feedback, Proceedings of Allerton Conference on Communication, Control, and Computing (Allerton), pp 203-210, September 2013.


[D3] Jingwen Bai (PhD, Advisor: PI Sabharwal), Wireless Side-channels in MIMO Full-duplex Systems, Rice University, 2016 .
[D2] Evan Everett (PhD, Advisor: PI Sabharwal), Full-duplex Wireless with Large Antenna Arrays, Rice University, 2016
[D1] Xu Du (MS, Advisor: PI Sabharwal), MIMO Broadcast Channels with Full-duplex Feedback , Rice University, 2015


[B1] Salman Avestimehr, Suhas N. Diggavi, Chao Tian, David N. C. Tse (2015). An Approximation Approach to Network Information Theory. Foundations and Trends in Communications and Information Theory. NOW publishers.